The present invention relates to a deflecting roller for sensing the distribution of stress along the roller while the roller deflects a strip of sheet material, and in particular, an improved deflecting roller having a plurality of stress sensors disposed around the roller such that the stress sensors sense the radially acting force on the roller, without contributing any interfering forces thereto.
Deflecting rollers having means for measuring the distribution of stress along the roller, are known. Such rollers frequently are used to measure stress, and the resulting measurements are then used to control an operating sequence in a final rolling process of a valuable sheet metal product.
As an example, German Patent No. 2,944,723 discloses that, in a hollow roller comprised of rings held together by a plurality of screws, measurement error can be decreased by appropriately flexing the roller. This is achieved by modifying the form of the deflecting roller to comprise a combination of discs having different shapes, and this, in turn, provides better structural adjustments in the sag zones and also provides improved resistance to sagging in the peripheral zones. Although deviations in the transverse strain due to elastic deformation are slight, they nevertheless lead to errors in the measurement of stress distribution. The circular cross sectional shape of the deflecting roller tends to deform to an egg shape or obloid when under stress, with the larger radius being at the locus where the bending force is exerted on the strip of sheet material. Consequently, the peripheral zones of the roller are successively stretched and compressed, in the direction in which the bending force acts, and as a result of this stretching and compressing, force sensors are stressed in such a way that additional forces and moments are transmitted to each sensor via the covers thereof. These forces are typically referred to as "interfering radial forces".
The cover for each force sensor has a major effect on the accuracy of measurements. With reference to FIG. 1D, in the case of a membrane cover 3 integrally formed with the roller 4, effective placement circumferentially around the roller 4 can be obtained by way of contact between the opposite ends of the sensor 1 and the measuring roller 4 itself. FIG. 1C illustrates placement by way of a thermal shrink ring 3, while FIGS. 1A and 1B illustrates a tensile/compressive disc-shaped cover 3. Though the arrangements of FIGS. 1A-1C are generally effective in the radial direction, the covers can become separated from the measurement rollers by gaps. In addition to the forces to be measured, the above-mentioned types of covers therefore transmit forces and moments to the sensor 1 which include interfering radial forces. The arrows in FIG. 2 denote these forces and moments which contribute the interfering radial forces.
The radial forces on each sensor 1 also undergo spurious secondary variations in the event of temperature changes, such as when the roller 4 surface is heated by the sheet material 8. When heating occurs, the roller surface flexes more than the core, resulting in thermal deformation and strain, and thereby generating interfering forces on the cover 3 of the force sensor. Interfering forces of this type are very costly to eliminate, if they can be eliminated at all. One such costly technique is to provide force sensors distributed over the entire circumference of the roller, which sensors have positive and negative characteristic curves and are electrically connected to one another. Likewise, reset circuits can be employed, wherein the interfering signal is set to zero when a certain limit is exceeded.
In addition to deformation of the measuring rollers 4 due to temperature changes, there also may be deformations of the rollers due to flexural (transverse) stresses when the radial forces acting on the rollers 4 are relatively large. Compensating circuits employed in the conventional measuring rollers described above achieve the required compensation by arranging force sensors at the periphery of each roller, at diametrically opposite positions (180 degrees with respect to one another). These diametrically opposed force sensors are interconnected, so that the starting point of the measurement is equal to the bending moment stresses. Such an arrangement, although generally effective, entails substantial investment costs.